1. Field of the Invention
This invention pertains generally to an energy efficient axial fan for exhausting humid, corrosive and dusty air from a variety of buildings, including, by way of example: foundries, manufacturing facilities, poultry operations, green houses, etc. . . .
More particularly, the present invention relates generally to new and useful improvements of axial fans comprising a shutter operated by a centrifugal mechanism.
2. Description of the Prior Art
Most axial fans are provided with gravity shutters. They are closed by gravity and opened by the airflow exiting the fan. When said fans operate in dusty atmospheres, if air velocity across the shutters is lower than the minimum velocity to prevent dust settling, said dust quickly accumulates on the shutters increasing the overall weight of the shutters. The heavier the shutters are, the harder it is for the fan to blow air through them. As a result, the fan moves less air and efficiency is reduced. Therefore, gravity shutters need routine cleaning but, after cleaning them, just after a few days of operation, they are once again covered with dust and one can clearly see them hanging at an angle, partially closed again. During the cleaning operation, it is possible to damage them resulting in shutters not closing or opening completely.
Cleaning the shutters is a difficult task and therefore, they are not cleaned as often as they should. Dust build up creates undesirable flow restrictions, which reduces the airflow capacity of the fan and affects the opening and closing of the shutters. As a result, it causes undesirable air infiltrations and building heat losses.
The air moving capacity of a fan with gravity shutters is also negatively affected by stormy weather. If a strong wind hits the operating fan, the shutters close partially. The wind lets up and the shutters open again. When the fan is off, high winds can open said shutters admitting unexpected cold or warm air into the building or allowing the inside air to escape therefrom.
When the fan with gravity shutters is operating, there is always a “constant battle” between the airflow blowing the shutters open and the gravity forces trying to close them. This results in a continuous oscillation of the shutters, pressure losses, waste of energy, vibrations, wear and reduction of airflow.
An axial fan is provided with a housing enclosing a fan comprising a motor and a propeller coupled thereto. Said propeller comprises a plurality of radial blades having tips running at close distance with a Venturi or orifice.
Enhancing the state-of-the-art in air moving axial fans mainly focuses on three directions: First, the ability to smoothly transmit the air from the intake opening of the fan housing into the inlet side of the Venturi and the propeller. Second, the ability to decrease the gap between the said Venturi and the said propeller blades tips. Third, the ability to provide the propeller and other elements exposed to airflow with airfoil shaped surfaces. Airfoil shaped blades assure the quietest and most efficient operation of the fan.
In conventional axial fans, due to the limited capabilities of the prior techniques in manufacturing and producing with precision fan housings and Venturi, the performance of the fans has been limited. Designers were obliged to leave a relatively large tip blade clearance to accommodate imperfection of manufacturing and thermal variations and expansions of the propeller blades and or the Venturi for preventing, in same situations, the fan blades to come into contact with said Venturi. Many studies show that the larger this space is, the lower the fan efficiency.
Motorized shutters or centrifugal shutter systems have been successfully utilized to solve the problems of said gravity shutters. The motorized shutters are relatively expensive; therefore the art has developed various centrifugal systems to operate said shutters, to fully open and keep them positively open in spite of the inevitable dust accumulation thereon and stormy weather.
The use of said centrifugal systems enhance the fan performance because said devices open the shutters wider and because the air pressure losses of said conventional gravity shutters, caused by the out-flowing air required to keep said shutters opened, are eliminated. Air is allowed to flow unobstructed through the positively wide-pen shutters.
Using a centrifugal device translates to significantly reduce the workload of the drive motor. This allows a reduction of energy or reallocation of this power surplus.
A thorough description of the prior art known to the Applicant which is pertinent to the present application is described in the following patents:
INVENTORU.S. Pat. No.DATA GRANTEDMancinelli4,217,816August 1980Gigola5,195,928March 1993Mancinelli5,288,202February 1994Milana6,276,895August 2001
In the known art, better described in U.S. Pat. No. 6,276,895 by this Applicant, the problems of vibrations and rattling were solved, but dust accumulation and air leakage from the shutters were not.
The fans with centrifugal devices of the prior art include an electric motor, a propeller and a shutter assembly comprising of a plurality of horizontal extending shutters or vanes including a central operative vane located in proximity to the propeller. The centrifugal devices of Mancinelli comprise of two centrifugal masses whereas the one of Gigola comprises three masses rotating with the propeller. As soon as the drive motor of said fans starts, the propeller speeds up, therefore the rotating masses move outwardly radially away from the fan axis of rotation due to centrifugal action. Through a series of complex linkages, the movement of the masses forces the shutter wide open even in stormy weather. As the fan shuts off, the centrifugal masses move back toward the propeller rotational axis. As a result, the vanes of Mancinelli, assisted by springs, firmly close, while the vanes of Gigola close by gravity.
While having these and other advantages, the fans of Mancinelli and Gigola have some disadvantages. For example, the centrifugal mechanism needs routine maintenance and their horizontal disposed vanes must be cleaned regularly. Said vanes are disposed at the fan exhaust where air velocity is relatively higher than at the intake; so the pressure losses are greater and efficiency is reduced.
In addition, the above centrifugal devices comprise an axially sliding actuator rotatably connected with the shutter central operative vane for transmitting, through complex linkages, the centrifugal forces of said masses. Therefore, the actuators transmit to said shutter the vibrations of the propeller as well as the vibrations of the centrifugal mechanisms. Moreover, when said fans are in operation, said mechanisms push continuously the shutter via a thrust bearing. For that reason, said vanes are subject to continuous friction, oscillations and wear.
None of the known fans of the prior art solves the problems of dust settling on their horizontally disposed shutters or vanes. In addition, none of said fans have the unique feature of the fan of the present invention.
There remains the need for a fan with a self-cleaning shutter suitable to prevent the usual dust accumulation on the shutters of the prior art fans. The Applicant in effect finds that designing the shutter with vertically extending vanes serves to overcome the problem of dust settling on the shutters so to achieve a self-cleaning effect. However, a shutter with vertical pivoting vanes must be operated by a device, for example a centrifugal mechanism.
Various studies from many Universities for poultry house buildings show that dust accumulation on conventional shutters of prior art fans can cause a reduction of the airflow by 30%. If said fans move 30% less air than they should, more fans are required to do the work resulting in higher electricity bills and increased wear on said fans.
The farm buildings usually require a large number of fans which, during hot weather, operate 24 hours a day and therefore require a significant energy use. Thus, it is important to solve the dust problem on shutters to ensure high operating efficiency and a maintenance free fan with improved self-cleaning shutters or vanes to conserve electrical energy over the long period that the fan is operated.
There is a need and a demand for a high energy efficient practically maintenance free fan with the unique features described hereinafter.